Segontium was a Roman fortress that was founded in 77 and 78 AD by Agricola after he had conquered the Ordovices in Northern Wales. It was the main Roman fortress in the north Roman Wales. The fortress was connected by a Roman road to the Roman legionary base at Chester (Deva Victrix).
Much of the fortress remains today. The A4085 cuts right through the centre of the fortress. Sections of the walls that surrounded the fortress remain together with foundations of civilian buildings. A Roman temple of Mithras (Caernarfon Mithraeum) and a cemetery have also been discovered at the site.